Liquid cooled engine

ABSTRACT

A novel engine cooling system which incorporates a special heat exchanger. The heat exchanger replaces the conventional exhaust inlet or inlet manifold of an internal combustion engine. The heat exchanger includes an exhaust conduit having an inlet portion, an intermediate portion and an outlet portion. Encompassing walls define two separate flowpaths for coolant such that the coolant is in thermal communication with the exhaust conduit. A first one of these passages extends only over the inlet portion of the exhaust conduit; the other of the coolant passageways extends over the intermediate and outlet portions of the conduit although it can, and, in the embodiment shown, does extend over the inlet portion as well. The heat exchanger is connected to receive exhaust gases from the engine. Its coolant passageways are connected in a circuit which includes an inlet by which make-up water is introduced into a pump which forces fluid through the first passageway of the heat exchanger into the cooling passages of the engine from whence it is circulated back to the inlet side of the pump when the coolant has a temperature below a selected value. When the coolant temperature rises above that value, it is permitted to flow past a thermostatic valve to the second coolant passageway of the heat exchanger, after which it is exhausted to the exhaust gas stream. The heat exchanger is oriented so that one portion of the second coolant passageway is disposed above other portions and the conduit is arranged so that flow is confined at one point along the length of the exhaust conduit to flow in the region of that uppermost point whereby the second fluid passageway is maintained substantially full of coolant from that point upstream.

Unite @fiates E teiit- [191 Fish [ Oct. 16, 1973 LIQUID COOLED ENGINE[76] Inventor: Robert F. Fish, 877 W. 17th St.,

Costa Mesa, Calif.

[22] Filed: Jan. 28, 1971 [21] Appl. No.: 110,727

Primary ExaminerCharles Sukalo Attorney-Nienow & Frater [57] ABSTRACT Anovel engine cooling system which incorporates a special heat exchanger.The heat exchanger replaces the conventional exhaust inlet or inletmanifold of an internal combustion engine. The heat exchanger includesan exhaust conduit having an inlet portion, an intermediate portion andan outlet portion. Encompassing walls define two separate flowpaths forcool- WITH COOLING PASSAGES I O8 ENGINE BLOCK ant such that the coolantis in thermal communication with the exhaust conduit. A first one ofthese passages extends only over the inlet portion of the exhaustconduit; the other of the coolant passageways extends over theintermediate and outlet portions of the conduit although it can, and, inthe embodiment shown, does extend over the inlet portion as well. Theheat exchanger is connected to receive exhaust gases from the engine.lts coolant passageways are connected in a circuit which includes aninlet by which make-up water is introduced into a pump which forcesfluid through the first passageway of the heat exchanger into thecooling passages of the engine from whence it is circulated back to theinlet side of the pump when the coolant has a temperature below aselected value. When the coolant temperature rises above that value, itis permitted to flow past a thermostatic valve to the second coolantpassageway of the heat exchanger, after which it is exhausted to theexhaust gas stream. The heat exchanger is oriented so that one portionof the second coolant passageway is disposed above other portions andthe conduit is arranged so that flow is confined at one point along thelength of the exhaust conduit to flow in the region of that uppermostpoint whereby the second fluid passageway is maintained substantiallyfull of coolant from that point upstream.

11 Claims, 7 Drawing Figures PAIENTEDncI 16 I975 sum 1 OF 3 INVENTORROBERT F. FISIH ENGINE. BLOCK 54 5 WITH COOLING 94 PASSAGES BY w HMATTORNEYS PATENTEDUCI 16 ms 3, 765479 SHEET 2 BF 5 INVENTOR ROBERT FFISH ATTORNEYS PATENTED OCT 16 I975 3.765.419 SHEET 3 SF 3 ATTORNEYSLIQUID COOLED ENGINE This invention relates to improvements in liquidcooled engines and it relates particularly to an improved engine formarine application.

One of the objects of the invention is to provide an improved liquidcooling system for engines which combines the engine and its coolantpassageways with conduits, pumps, valves and a heat exchange structurear ranged for preheating liquid coolant before introduction into theengine passages and for cooling the conduit by which exhaust gases arelead from the engine. Provision of that novel structure, and provisionof the novel cooling system made possible by its combination with anengine, are both objects of the invention.

It will be apparent that the invention is not limited to use inconnection with inboard marine engines. However, the invention isespecially well-adapted for that application. Accordingly, it is one ofthe objects to provide an improved cooling system circuit and structurefor that application. In certain classes of boats, it is advantageous tomount the propulsion engine back adjacent to the transom for directconnection to a steerable propeller drive and propeller. Locating theengine in that fashion introduces a number of problems. Special designis ordinarily required to ensure that the engine structure imposes noserious limitation on the steering system. In addition, spacelimitations ordinarily require that the engine enclosure be as small aspossible and that boat occupants be seated and that gear be placedimmediately adjacent to the engine. That spatial limitation gives riseto the requirement that engine heat be minimized by use of an effectiveand efficient cooling arrangement. The exhaust gases, in the case ofmost engines, are exhausted from a series of space ports. Consequently,the manifold in which they are collected for explusion outside the boatextends substantially over the whole length of the engine and is exposedat the interior of the engine. In the case of V8 engines two suchmanifolds are employed. One of the objects of the invention is to makeit more feasible to employ an engine of conventional design whichrequires large, exposed exhaust gas collection manifolds. A relatedobject is to provide an engine and engine cooling system for limitingthe maximum engine temperature and for greatly reducing exhaust conduittemperature.

These and other objects and advantages of the invention are realized bythe combination with an engine of the kind that has exhaust ports andinternal passageways for fluid coolant of a heat exchanger meanscomprising an exhaust gas conduit formed by an inner wall and extendingfrom the region of the engine exhaust ports to an intermediate gas flowconducting portion and then to an outlet section for discharging thatexhaust gas and, which further comprises a jacket formed by said innerwall and an overlying outer wall, the outer wall being arranged todefine two separate passageways FIG. 1 is a pictorial view of a marineengine which is fitted with the cooling circuit of the inventionincluding the novel heat exchanger structure that it provides;

FIG. 2 is a diagram of the cooling system circuit employed in the engineof FIG. 1;

FIG. 3 is a pictorial view of the novel heat exchanger employed in theinvention;

FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 3;

FIG. 5 is a cross-sectional view taken on line 55 of FIG. 3;

FIG. 6 is a cross-sectional view taken on the vertical, longitudinalmidplane of the U-shaped portion of the heat exchanger of FIG. 3, exceptthat portions have been cut away to expose the nature of the doublewalled construction; and

FIG. 7 is a cross-sectional view taken on line 7-7 of FIG. 6.

The engine selected for illustration in FIG. 1 is an internal combustionunit which uses gasoline as fuel and is generally of the same type andstyle as the engines used in passenger automobiles. The engine isgenerally designated 10. Its block 12 is provided with internalpassageways by which a coolant may flow. A pulley 14 at the lower,forward end of the engine is driven by the engines crankshaft. A belt 16transmits power from that pulley to a cam driven pump 18 by whichcoolant is pumped through the system. The numeral 20 designates an airfilter; the element 22 is the oil pan.

Thus far described the unit does not differ materially from an ordinaryautomobile engine. The exhaust manifolds do differ, however. They areheat exchangers. In this case it has been assumed that the engine is ofthe V8 variety with four exhaust ports at the right and four at theleft. The right exhaust manifold heat exchanger structure is designatedby the numeral 24 and the left one is designated 26. In this embodimentthe exhaust gas is expelled from the heat exchanger through a flexibleconduit 28 through an opening in the boats transom.

The boats transom was omitted from FIG. 1 so that the propeller 30 andthe propeller drive housing 32 would be visible. A part 34 of thetransmission s system is mounted forward to the transom and theremainder is mounted behind it. Thus, the transom is placed justrearward of the U-shaped portions 36 and 38 of the two heat exchangers.

The boat may be steered by pivoting the propeller drive housing 32 abouta pivot axis rearward of the transom. The force by which it is made topivot is applied to a tiller arm 40 which is arranged to extend throughor over the transom. Steering cables 42 extend in opposite directionsfrom a connection to the end of the tiller bar 40 through the spacesdefined by the U- shaped rear sections 36 and 38 of the two heatexchangers. Guides for those cables are attached to the housing withinthose spaces. This arrangement is particularly advantageous. The U-shapeof the heat exchanger structure is doubly functional in that it ensuresa generally uniform high degree of exhaust gas cooling, as well asproviding protection for, and against, the tiller bar while providing ahigh order of stability for the steering cable system in the region oftiller bar movement.

The heat exchangers both include a passageway or conduit for exhaustgases and two liquid coolant passageways. The inner exhaust conduit isjacketed to form a double walled arrangement. Exhaust gases flow in theconduit defined by the inner wall and the cooling liquid flows in thespace between the double walls. That space is divided by blocking wallsinto two flowpaths. The exhaust conduit is connected to the exhaustports of the engine by laterally and downwardly extending connectingconduits that are not visible in FIG. 1. They can be seen in FIG. 3 andone of them is shown in crosssection in FIG. 5. The exhaust conduitextends over the length of the engine and through the U-shaped sectionof the heat exchanger housing to an exit point at its junction with theflexible conduit 28. One of the liquid passageways, in this embodiment,extends only part way over the length of the exhaust conduit. It extendsover that part, called the inlet region, where the exhaust gases arecollected. Flow lines connected to the exchanger structure at both endsof that passage are connected at thier opposite ends to fittings at theforward end of the engine block. The two conduits associated with heatexchanger 26 are identified in FIG. 1 by the reference numerals 44 and46. Another conduit 48 interconnects the inner passages of the engineblock with the other liquid flow passage in exchanger 26. Thatpassageway has an outlet near the outlet of the exchanger at the pointof its connection with flexible conduit 28.

The interconnection of the engine pump, control valve, and the severalconduits with the passageways of the manifold structure is illustratedin FIG. 2. In that figure, the engine block and its cooling passages areillustrated by a block 50. The engine block is provided with fourexhaust gas outlet ports on each side. For identification, one of thoseoutlet ports has been designated 52 in FIG. 2. The lateral, connectingconduit 54 leads from that exhaust port opening to a port 56 which opensto the interior of the heat exchange structure 24. The preferredarrangement is illustrated in detail in FIG. 5.

Pump 18 of FIG. 2 is the same one designated 18 in FIG. 1. The exhaustgases are collected in the exhaust conduit which is formed by an innerwall generally designated 58 in FIG. 2. Those gases pass through theconduit moving rearwardly through the U-shaped section 36 of thestructure and then emerge at the junction with the flexible conduit 60.The latter is like the flexible conduit 28 with the exception that it isconnected to the other of the two heat exchangers.

The exhaust conduit portion of the exchanger is conveniently consideredto comprise three portions. The first is called an inlet portion and isthat portion of the conduit in which the exhaust gases are collected. In

general, that part extends from the forward end of the exhaust conduitto a point just downstream of the rearmost of the exhaust inletopenings. The numeral 62 in the case of U shaped member 38, and thenumeral 64 in the case of U-shaped member 36, identify a dam in one ofthe two liquid flow passageways. The'portion of the exhaust conduitwhich lies upstream from the vicinity of that dam, and downstream fromthe inlet portion is called the intermediate portion. That portion ofthe exhaust conduit which lies downstream from the vicinity of the damis called the exhaust or outlet portion.

The liquid passageways are formed by the double walls of the exchangerstructure. In the case of manifold 24 the inner walls are generallydesignated 58. Together with a portion of the outer wall that isidentified by the reference numeral 66, the inner wall 58 defines apassageway in which cooling liquid is preheated. This passageway,numbered 68, is called the preheating passageway. Another portion of theouter wall cooperates with wall 58 to define a second passageway forliquid coolant which is called the exhaust conduit cooling passageway"or cooling passageway 72. In this embodiment the preheating passagewayextends approximately the length of the inlet portion of the exhaustconduit. The cooling passageway extends over the intermediate portion ofthe exhaust conduit and over at least part of the exhaust portion ofthat conduit. It may, and in this embodiment it does, extend over theinlet portion of the exhaust conduit as well. In the intermediateportion of the exhaust conduit, the cooling passageway 72 extendssubstantially entirely around the exhaust conduit and the passageway hasbeen extended in the diagram to the inner region of the U- shapedsection 76 to illustrate that this is so.

The arrangement of the other exhaust manifold structure 26 is similar.For identification, walls that define the exhaust conduit are generallydesignated 74. The wall that cooperates with that inner conduit to formthe exhaust conduit cooling passage 76 is desig- I nated 78. The wallthat cooperates with inner wall 74 to form the precooling passageway 80is designated by reference numeral 82. The inlet to that passage isdesignated 83 and the outlet is numbered 84. The inlet 85 of the exhaustconduit cooling passageway is at the forward end of the structure andthe outlet 86 is at the rearward end adjacent the connection with theflexible conduit 28. In the lower part of FIG. 2 the precoolingpassageway has an inlet 86 and an outlet 87. The exhaust conduit coolingpassageway has an inlet 88 and an outlet 89. The engine block coolingpassage system includes inlets 91 and 92. It includes a recirculationoutlet 90, a primary outlet 94 and a safety bypass passageway 95. Thatoutlet bypasses the thermostatic valve 96. That valve is connected inseries between outlets 94 and the inlets 85 and 88 of the two exhaustconduit passageways. Valve 96 and inlet 85 are interconnected by theconduit 48 which was visible in FIG. 1. The valve 96 and inlet 88 areconnected by a conduit 98. Outlet 84 and engine block unit 92 areinterconnected by the conduit 46. On the other side of the engine,engine block inlet 91 and precooling passage outlet 87 areinterconnected by a conduit 100. The outlet side of pump 18 is connectedto precooling passageway 80 by the conduit 44 and is connected to theinlet opening 86 of the other precooling passageway by a conduit 102.Cooling water, either sea water or fresh water, enters the system at aninlet 104 and is conducted by a passageway 106 to the inlet side of pump108. The recirculation outlet is connected by a conduit 108 back to theinlet side of the pump.

Make-up water enters in at inlet 104 and proceeds by conduit 106 to theinlet side of pump 18 where it is forced through conduits 44 and 102 toenter into the precooling passageways 80 and 68. The water flows throughthose passageways and emerges at outlets 84 and 87. It then proceeds byconduits 46 and 100 to engine -block inlets 92 and 91, respectively.Until that cooling water has reached a temperature sufficiently high toopen the thermostatic valve 96, it exits the engine at outlet andtravels by conduit 108 to the junction with conduit 106. Thereafter, itagain flows to the inlet section of pump 18 to be recirculated throughthe preheating passageways 80 and 68. When this circulating water hasreached a temperature sufficiently high to open the thermostatic valve96, then the water is free to flow from the engine to conduits 48 and 98to inlets 85 and 88 of the two exhaust conduit cooling passageways 76and 72. Those passageways must become entirely filled with waterdownstream of their respective dams 62 and 64, before any of the waterthey contain can be expelled to that portion of the passageway thatsurrounds the outlet section of the exhaust conduit. This result isachieved by providing the heat exchange structure with a downstreamsection that is placed generally above and higher than any other sectionof the exhaust system. That section could be U-shaped, V- shaped, orotherwise shaped to accomplish that result. In the preferred embodiment,the U-shape is employed because it provides a number of advantages. Itremoves the cooling function to the very rear of the boat, or at leastto the rear of the engine; it provides a very effective and efficientmeans for protecting the tiller linkage and for guiding the steeringcables; and it has certain manufacturing advantages.

The cooling circuit arrangement offers a number of advantages. It isdesirable to have the heat rise in the engine block occur as uniformlyas possible following engine start-up. The invention helps to achievethat result by precirculating the water contained in the engine blockpast the hottest portion, the inlet portion, of the exhaust conduit. Inthe preferred form, that passageway is limited substantially to theinlet portion of the exhaust conduit as illustrated in FIG. 2. It willbe shown subsequently, in examination of FIG. 5, that the preheatingpassageway encompasses a larger portion of the inlet portion of theexhaust conduit than does the cooling passageway. The result is rapidpreheating of the cooling water. During initial operation that featurehelps raise engine block temperature uniformly and rapidly.Subsequently, it minimizes extreme thermal differences by preventingdirect introduction into the heated block of very much colder sea water.A further advantage is that the coolant that flows through the preheatedpassageway derives its heat from the hottest part of the exhaust conduitso that excessive heat rise is avoided.

In most small boat designs, the engineoccupies a premium space. Theengines themselves are available in compact form. However, the spacethat must be devoted to the engine is function not only of engine sizebut is also a function of engine temperature. If the temperature can beminimized, the size of the engine compartment 0r enclosure can bereduced. In large mea.

sure, the size of that compartment is determined by maximum enginetemperature rather than by average temperature. Accordingly, it isdesirable to provide an engine cooling system which minimizes peaktemperature as well as average temperature. Efficiency demands that thecooling system contribute to engine warm-up. Within the engine itself,these antithetical requirements are dealt with by the thermostaticvalve. In this case, it is desired not only to control block temperaturebut also to control exhaust conduit temperature. Here, too, therequirements are different during the start-up and the run condition. Inthis case, the invention solves the problem by the special arrangementof its exhaust manifold and heat exchange structure and by thecombination with that structure of the thermostatic valve and the flowcircuit arrangement. During the start-up period, the short but largearea preheating passageway provides the heat input necessary to ensurethe requisite degree of block temperature uniformity. The preheatingpassageway is assisted in its function by the thermostatic valve whichensures recirculation of the coolant with minimum introduction of coldwater. After the engine is heated, the coolant is expelled from thesystem and new coolant is introduced. That new coolant has a much lowertemperature and serves to carry away large quantities of heat from thehottest, inlet section of the exhaustconduit. The cooling passage of theexchanger is supplied with coolant only after the engine is heated. Itcompletely surrounds the intermediate portion of the exhaust conduit toensure that a maximum volume of water is exposed, through a maximum heatexchange surface, to the heat of the exhaust gases. The cooling passageis extended forwardly adjacent the inlet portion of the exhaust passageto the extent that the surface area of the exhaust conduit does not needto be encompassed by the preheating conduit. In this embodiment,approximately onefourth of the conduit wall in the inlet portion forms apart of the cooling passageway while three-fourths of that wall forms apart of the preheating passageway. The heat exchange structure isoriented so that dams 62 and 64 are at an uppermost point thereby toensure that the passageway is completely filled with coolant upstreamfrom that point. Below the dam, the coolant is finally expelled into thestream of exhaust gases, cooling those gases sufficiently so thatflexible conduit of conventional material can withstand theirtemperatures.

A preferred heat exchange structure is shown in FIGS. 3 through 7. Thewhole structure 24 is shown in FIG. 3. It comprises a straight section110, having an end closure 112 at its forward end, and the U-shapedsection 36 at its rearmost end. The three sections are cast separatelyand are bolted together. Bolts 114 connect the forward closure to thestraight section 112 and the bolts 116 connect the U-shaped section tothe straight section. There are four inlet conduits that affordcommunication for exhaust gases from the exit ports of the engine to theinlet section of the exhaust conduit. The conduit 54 is the one that wasidentified in connection with the description of FIG. 2 and is the oneshown in cross-section in FIG. 5. The exit opening for the exhaustconduit is designated 118 and it is on this element that the flexibleconduit 60 is fitted. The flexible conduit has been omitted from thefigure so that the outlet opening 86 of the coolant passage is madevisible. The threaded boss 120, which can be seen on the upper innersurface of the U-shaped section 36, accommodates a fitting through whichthe steering cable is run. Just below that, the numeral 122 identifies adrain port for the cooling passageway. At the front closure 112, elbow124 is connected to the inlet opening and forms part of conduit 48. Justbelow, the nipple 126 forms part of the coolant passage outlet opening84.

In this embodiment, the cooling passage extends over the length of thestraight section 112' and it continues into the lower forward portion ofthe U-shaped section 36. Except in the region of the four passageways bywhich exhaust gases are admitted into the exchanger, the preheatingpassageway extends between the double walls of the structure at itssides and at its bottom. Thus, in FIG. 5 the exhaust conduit is definedby the inner walls 58. The cooling passageway is defined by the lowerone and the side ones of those inner walls and by the outer walls 66 atthe sides and the bottom of the structure. The coolant passage is theupper one in FIG. and is defined by the upper wall 58 at its inside andthe wall 70 at its outside. The passageway is necked down at 130 becausethe outer wall is indented to accommodate the bolts 114.

That the two passageways are separated is illustrated by thecross-sectional, pictorial view of end member 1 12 in FIG. 4. The slot132 communicates only with the upper coolant passage of the straightsection 110 and with the elbow 124. On the other hand, nipple 126communicates with the bottom and the side openings that comprise theprecooling passageways 68.

The rearmost region of the precooling passage is shown at the lower leftin FIG. 6. The cross-sectional view in that figure is taken on thevertical, longitudinal midplane of the U-shaped section 36. The far wallof this structure is double; part of it has been broken away to make itclear that the upper section of wall 58 extends throughout the length ofthe precooling passageway with respect to the coolant passageway eventhough the exhaust conduit turns upwardly and continues through portion58a of that wall. The inner wall has been broken away above the Webb 58ato show that from that point on downstream all of the space between theinner and outer walls is part of the cooling passageway. A dam is formedtransversely across that flow passage on the plane 7--7 of FIG. 6. Thedam is formed by a webb that interconnects the inner and outer wallsexcept at the upper portion of the space between them. The edge of thedam visible in FIG. 6 is designated 140. FIG. 7 is a cross-sectionalview taken on line 7--7 which illustrates this construction. Below thedam the cooling passageway encompasses the exhaust conduit over most ofits area so that additional cooling is accomplished.

The extent to which that passage is filled with water, and therefore theextent to which cooling is accomplished in that portion, depends uponthe size of opening 86 and the rate at which 18 forces coolant to flow.The pump 18 is driven at a speed that varies with engine speed. In amarine engine, engine load is rather directly related to engine speedand heating is rather directly related to engine load. As a consequence,if the outlet opening 86 is not unduly large, the amount of water in thefinal section of the cooling passage will vary with load and thequantity of heat that must be removed from the exhaust gases.

Advantageously, the dam is located at the highest point in the coolantflowpath so that the flowpath must be completely filled upstream fromthat point. Removal of the dam from that high point does not destroy thevalue of the invention although efficiency would be lowered somewhat.The dam may haveany convenient form. Thus, it could comprise any kind ofstructural division of the coolant passageway into upstream anddownstream sections interconnected at an elevated point. Y

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art.

I claim:

1. For use in cooling an engine which has an exhaust gas exit port andhas an inlet opening and an outlet opening for receiving and dischargingfluid, respectively:

a heat exchanger comprising an exhaust conduit formed by an encompassingwall and defining an inlet portion for receiving exhaust gas from theengine exit port, an intermediate portion, and an outlet end portion fordischarging exhaust gas that has traversed said intermediate portionafter entering at the inlet portion;

a jacket comprising said encompassing wall and an overlying outer wall,said jacket being formed to define two passageways capable of conductingliquid coolant, one of said passageways extending over the inlet portionof said exhaust conduit, the other one of said passageways extendingover the intermediate portion of said exhaust conduit; and

means interconnecting said heat exchanger and said engine such thatexhaust gas is permitted to flow to said exhaust conduit, coolant ispermitted to flow from said one passageway to said engine inlet, andfluid from said engine outlet is permitted to flow to said other one ofsaid passageways.

2. The invention defined in claim 1 in which said other one of saidpassageways is formed with an outlet openingwhich opens at the interiorof said exhaust conduit.

3. The invention defined in claim 2 in which said jacket furthercomprises means for insuring that said other one of said passageways issubstantially completely filled with coolant along an initial portion ofits length before fluid can be discharged from said outlet opening.

4. The invention defined in claim 1 in which said jacket comprises meansfor insuring that said other one of said passageways is substantiallycompletely filled with coolant along an upstream portion of its length,said means comprising mounting means for mounting said conduit with oneportion of said other one of said passageways uppermost and of dam meansin the form of a darn interconnecting said inner and outer walls exceptin the region of said one portion of said other of said passageways forconfining flow to that one portion.

5. In combination:

an elongate exhaust conduit comprising an inlet section, an intermediatesection and an outlet section, said conduit being formed with openingsin its inlet section by which exhaust gases may be admitted thereto sothat they will traverse the conduit from its inletsection through itsintermediate section to be expelled at said outlet section;

means comprising a first enclosing wall overlying portions of saidexhaust conduit at its inlet section and defining'a first passageway forcoolant having inlet and outlet openings;

means comprising a second enclosing wall overlying portions of saidconduit at its intermediate section and at its outlet section anddefining inlet and outlet openings; and

means for orienting said conduit and enclosing walls such that oneportion of the flowpath formed by said conduit and said second enclosingwall is uppermost in the vicinity of the juncture of said intermediatesection and said outlet section of said conduit and for confining flowof fluid along said second passageway to flow substantially at saiduppermost region.

6. The invention defined in claim together with an engine comprising aplurality of spaced exhaust gas outlet ports, an inlet opening forcoolant, an outlet opening for coolant, and internal passagewaysinterconnecting said inlet and said outlet;

means interconnecting the outlet ports of the engine with the openingsin the inlet section of said exhaust conduit;

' means for connecting said first passageway and the passageways throughsaid engine and said second passageway in series, in that order,comprising a first conduit extending from said first passageway definedby said first overlying wall to the inlet of said engine, and comprisinga second interconnecting conduit extending from the outlet of saidengine to said second passageway defined by said second overlying wall.

7. The invention defined in claim 6 together with means for forcing aflow of coolant into said first passageway and for permitting flow ofcoolant from said passageways of the engine to said second passagewaywhen said coolant has a temperature exceeding a selected value.

8. The invention defined in claim 7 in which said first passageway isconfined to the inlet area of said exhaust conduit and in which saidsecond passageway extends throughout the length of said exhaust conduit.

9. The invention defined in claim 6 in which said conduit comprises ahorizontal section and an inverted U- shaped section, said firstenclosing wall overlying the horizontal section and said secondenclosing wall overlying the inverted U-shaped section.

10. The invention defined in claim 9 in which said U- shaped sectioncomprises a double-walled jacket and said means for confining the flowto said one portion of said'second passageway comprises a dam disposedbetween the walls of the conduit and the second overlying wall except atan upper region of said U-shaped sec tion.

11. The invention defined in claim 9 which further comprises an inletconduit for make-up water connected to the inlet side of said pump,means interconnecting the passageways of the engine with the inlet sideof said pump, said means for permitting flow of coolant from the enginepassageways to said second conduit comprising a thermostatic valve.

1. For use in cooling an engine which has an exhaust gas exit port andhas an inlet opening and an outlet opening for receiving and dischargingfluid, respectively: a heat exchanger comprising an exhaust conduitformed by an encompassing wall and defining an inlet portion forreceiving exhaust gas from the engine exit port, an intermediateportion, and an outlet end portion for discharging exhaust gas that hastraversed said intermediate portion after entering at the inlet portion;a jacket comprising said encompassing wall and an overlying outer wall,said jacket being formed to define two passageways capable of conductingliquid coolant, one of said passageways extending over the inlet portionof said exhaust conduit, the other one of said passageways extendingover the intermediate portion of said exhaust conduit; and meansinterconnecting said heat exchanger and said engine such that exhaustgas is permitted to flow to said exhaust conduit, coolant is permittedto flow from said one passageway to said engine inlet, and fluid fromsaid engine outlet is permitted to flow to said other one of saidpassageways.
 2. The invention defined in claim 1 in which said other oneof said passageways is formed with an outlet opening which opens at theinterior of said exhaust conduit.
 3. The invention defined in claim 2 inwhich said jacket further comprises means for insuring that said otherone of said passageways is substantially completely filled with coolantalong an initial portion of its length before fluid can be dischargedfrom said outlet opening.
 4. The invention defined in claim 1 in whichsaid jacket comprises means for insuring that said other one of saidpassageways is substantially completely filled with coolant along anupstream portion of its length, said means comprising mounting means formounting said conduit with one portion of said other one of saidpassageways uppermost and of dam means in the form of a daminterconnecting said inner and outer walls except in the region of saidone portion of said other of said passageways for confining flow to thatone portion.
 5. In combination: an elongate exhaust conduit comprisingan inlet section, an intermediate section and an outlet section, saidconduit being formed with openings in its inlet section by which exhaustgases may be admitted thereto so that they will traverse the conduitfrom its inlet section through its intermediate section to be expelledat said outlet section; means comprising a first enclosing walloverlying portions of said exhaust conduit at its inlet section anddefining a first passageway for coolant having inlet and outletopenings; means comprising a second enclosing wall overlying portions ofsaid conduit at its intermediate section and at its outlet section anddefining inlet and outlet openings; and means for orienting said conduitand enclosing walls such that one portion of the flowpath formed by saidconduit and said second enclosing wall is uppermost in the vicinity ofthe juncture of said intermediate section and said outlet section ofsaid conduit and for confining flow of fluid along said secondpassageway to flow substantially at said uppermost region.
 6. Theinvention defined in claim 5 together with an engine comprising aplurality of spaced exhaust gas outlet ports, an inlet opening forcoolant, an outlet opening for coolant, and internal passagewaysinterconnecting said inlet and said outlet; means interconnecting theoutlet ports of the engine with the openings in the inlet section ofsaid exhaust conduit; means for connecting said first passageway and thepassageways through said engine and said second passageway in series, inthat order, comprising a first conduit extending from said firstpassageway defined by said first overlying wall to the inlet of saidengine, and comprising a second interconnecting conduit extending fromthe outlet of said engine to said second passageway defined by saidsecond overlying wall.
 7. The invention defined in claim 6 together withmeans for forcing a flow of coolant into said first passageway and forpermitting flow of coolant from said passageways of the engine to saidsecond passageway when said coolant has a temperature exceeding aselected value.
 8. The invention defined in claim 7 in which said firstpassageway is confined to the inlet area of said exhaust conduit and inwhich said second passageway extends throughout the length of saidexhaust conduit.
 9. The invention defined in claim 6 in which saidconduit comprises a horizontal section and an inverted U-shaped section,said first enclosing wall overlying the horizontal section and saidsecond enclosing wall overlying the inverted U-shaped section.
 10. Theinvention defined in claim 9 in which said U-shaped section comprises adouble-walled jacket and said means for confining the flow to said oneportion of said second passageway comprises a dam disposed between thewalls of the conduit and the second overlying wall except at an upperregion of said U-shaped section.
 11. The invention defined in claim 9which further comprises an inlet conduit for make-up water connected tothe inlet side of said pump, means interconnecting the passageways ofthe engine with the inlet side of said pump, said means for permittingflow of coolant from the engine pAssageways to said second conduitcomprising a thermostatic valve.